Polymers of 2-ketopentafluoropropanesulfonic acid and related acids with ethylene or fluorinated unsaturated monomers

ABSTRACT

2-Ketopentafluoropropanesulfonic acid is obtained as a product of the reaction of sulfur trioxide and ethyl pentafluoroisopropenyl ether or by transesterification from corresponding esters. Similar sulfonic acids may be obtained by the latter process. The new compounds are useful as monomers for producing polymers, particularly moldable, dyeable, fluoropolymers, and as cationic initiators, e.g., for tetrahydrofuran polymerization.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of my copending application Ser. No.602,756 filed Aug. 7, 1975, and now U.S. Pat. No. 4,160,780, issued July10, 1979.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to 2-ketopentafluoropropanesulfonic acid andrelated sulfonic acids, their preparation, and polymers made from thesame.

2. Prior Art

2-Ketopentafluoropropanesulfonic acid is shown by Bekker et al., 1.L(Inst. Elementoorg. Soedin., Moscow, USSR). Dokl. Acad Nauk SSSR 1974,217 (6), 1320-3 [(Chem)] (Russ); Chem Abstr 81, 169,052 (1974). Theyreport obtaining the compound by heating CF₂ ═C(CF₃)OSO₃ H.

SUMMARY OF THE INVENTION

The present invention provides ketoperfluorosulfonic acids of theformula ##STR1## where R and R², alike or different are fluorine orperfluoroalkyl of up to 4 carbons.

The invention also provides a process for preparing the sulfonic acid bytransesterifying the corresponding methyl or ethyl esters with a strongacid. The esters are made according to the teachings of coassigned Ser.No. 602,757, filed Aug. 7, 1975, and now abandoned.

The acids are useful as cationic initiators for tetrahydrofuranpolymerization. They are also useful comonomers to make dyeable polymerswith ethylene, vinyl fluoride, tetrafluoroethylene, trifluoroethyleneand vinylidene fluoride.

PREFERRED EMBODIMENTS OF THE INVENTION

In the present invention, 2-ketopentafluoropropanesulfonic acid (II) isprepared along with ethyl 2-ketopentafluoropropanesulfonate (III) byreacting sulfur tioxide with ethyl pentafluoroisopropenyl ether (I)according to the equation: ##STR2##

The reaction is generally carried out in liquid phase, at a temperatureof about -40° to about +100° C., 0°-50° being preferred. The reactiontime can be short, in many cases the reaction being substantiallycompleted within a few minutes at about 50°-100° C., but can be as longas a day, e.g., at about -40° C. to 0° C. Atmospheric pressure isgenerally preferred, but pressures up to 3000 psi can be employed.

A solvent is not necessary, but media of low reactivity towards SO₃ maybe used, especially halogenated solvents such as tetrachloroethylene and1,1,2-trichloro-1,2,2-trifluoroethane. An excess of either reactant maybe used if desired, but a ratio of the acyclic fluorovinyl ether to SO₃close to 1:1 is preferred. Isolation is generally effected bydistillation under reduced pressure.

Although the acid II is obtained directly as a coproduct in the reactionabove, greatly increased yields are available by transesterificationwith other acids which are stable toward the powerfully acidic IIaccording to the equations (R_(f) is a perfluorinated radical such asCF₃, C₃ F₇, etc.): ##STR3## Suitable acids for use astransesterification partners with III are the illustratedperfluoroalkylcarboxylic acids, e.g., trifluoroacetic acid and sulfuricacid. In general, any strong acid which is stable toward II and boilslower or significantly higher than the desired sulfonic acid may beused. To carry out the transesterification, either a crude reactionproduct mixture containing ester III or purified ester III is treatedwith the acidic transesterification partner and allowed to stand atabout 25° C. for a day or heated briefly at about 80° C. Pure II isisolated by fractional distillation.

Other ketosulfonic acids can be made by the transesterification processof this invention. Thus, methyl2-keto-1-trifluoromethyltetrafluoropropanesulfonate [Ex. 4 of Ser. No.602,757] will give ##STR4##2-keto-1-trifluoromethyltetrafluoropropanesulfonic acid, ontransesterification with H₂ SO₄ or trifluoroacetic acid. The compound##STR5## methyl 2-ketoheptafluorobutane-1-sulfonate, prepared bytreatment of perfluorobutanone-2 with trimethyl phosphite, to give2-methoxyheptafluorobutene-1 which is then reacted with sulfur trioxide,will give ##STR6## 2-ketoheptafluorobutanesulfonic acid.

The present acids, especially 2-ketopentafluoropropanesulfonic acid, areuseful as comonomers for providing sulfonic acid groups whenincorporated into polymers especially fluoropolymers. Such sulfonic acidgroups serve (for example) as dyesites in solid polymers which otherwisewould not accept a dye. A general formula for the polymers may bewritten as ##STR7## where n is 2-500 (n is the mole ratio of comonomerto sulfonic acid moiety) and R is H or CF₂ CH₃. The comonomer may beethylene, vinyl fluoride, vinylidene fluoride, tetrafluoroethylene ortrifluoroethylene. As shown in the examples below, the product is asolid, heat-moldable, dyeable, heat-stable copolymer, a molecular weightin excess of 50,000 being indicated.

The following examples illustrate the practice and utility of theinvention. Examples 1-4 show the preparation of2-ketopentafluoropropanesulfonic acid and Examples 5-7 show thepreparation of polymers from the acid. In the examples, temperatures arein degrees centigrade and percentages are by weight. F113 in Examples5-7 is Freon® 113, trichlorotrifluoethane.

EXAMPLE 1 Ethyl 2-Ketopentafluoropropane Sulfonate (III) and2-Ketopentafluoropropanesulfonic Acid (II)

A. Dropwise addition of 12.8 g (0.16 mol) of SO₃ to 29.0 g (0.165 mol)of ethyl pentafluoroisopropenyl ether (D. W. Wiley and H. E. Simmons, J.Org. Chem. 29, 1876 (1974)) resulted in an exothermic reaction.Distillation of the black reaction mixture gave 6.3 g (22%) of cruderecovered ether (identified by ir) and 20.2 g (49% conv. and 63% yield)of III, bp 47°-48° (12 mm).

Spectral properties fit ring-opened ester III as the structure. Ir(neat) 3.34 and 3.41 (satd CH), 5.60 (C═O), 7.09 (SO₂ O), 7.6-8.5μ(CF,SO₂): nmr ¹ H 4.59 (q, J_(HH) 7.2 Hz, 2,OCH₂), 1.51 ppm (t, J_(HH)7.2 Hz, 3, CH₃); ¹⁹ F-75.0 (t,J_(FF) 8.3 Hz, 3,CF₃), -107.4 ppm (q,J_(FF) 8.3 Hz,2,CF₂).

B. Reaction of 176 g (1.0 mol) of ethyl pentafluoroisopropenyl ether and88 g (1.1 mol) of SO₃ (Equation 1, above) was carried out similarly to Aabove, but at 0.5°. The colorless reaction mixture, which darkened onstanding overnight, was distilled to give 28.6 g (16% of crude recoveredvinyl ether, bp 46°-48°; 145.1 g (57% conv. and 68% yield) of III, bp48°-52° (12 mm); and a higher boiling cut composed mainly of II.Redistillation of the crude II gave 35.6 g (16% conv. and 19% yield) ofII bp 82°-82° (6.2 mm).

For II, ir (CCl₄ between CaF₂ plates) broad 3.3 and 4.2 (SOH), 5.58(C═O), 7.13₁₉ (SO₂ O), 7.5-9μ (CF,SO₂): nmr (neat) ¹ H 10.2 ppm (s,SO₂OH); F-76.2 (t,J_(FF) 7.5 Hz, 3,CF₃), -108 ppm (q,J_(FF) 7.5 Hz,2,CF₂).

Anal. Calcd for C₃ HF₅ O₄ S: C, 15.80; H, 0.44; F, 41.65; S, 14.06.Found: C, 15.95; H, 0.55; F, 41.55: S, 13.89.

EXAMPLE 2 Preparation of 2-Ketofluoropropanesulfonic Acid from EthylPentafluoroisopropenyl Ether, SO₃ and Trifluoroacetic Acid

17.6 g (1.0 mol) of ethyl pentafluoroisopropenyl ether was cooledbetween -5° and -10° C. and stirred while 50 g (1.0 mol) of SO₃ wasadded over a 1.5 hr period. The mixture was stirred at -10° for anadditional 30 min. and then allowed to stand overnight. Theyellow-orange product was warmed and gave an exothermic reaction whichwas controlled at temperatures below 40° by mild cooling. 125.4 g (1.1mol) of trifluoroacetic acid was added, and the mixture was allowed tostand overnight and then fractionally distilled. After the removal ofexcess trifluoroacetic acid and CF₃ CO₂ CH₂ CH₃, 99.2 g of crude2-ketopentafluoropropanesulfonic acid was obtained representing a yieldof 44%, b.p. 55-68 at 2.8 mm pressure.

EXAMPLE 3 Preparation of 2-Ketopentafluoropropanesulfonic Acid fromEthyl Pentafluoroisopropenyl Ether, SO₃ and H₂ SO₄

58.0 g (0.33 mol) of ethyl pentafluoroisopropenyl ether was cooled toabout -15° while 25.6 g (0.32 mol) of SO₃ was being added. The mixturewas stirred and allowed to warm. On heating to 47° for several minutesan exothermic reaction resulted, the temperature of the mixture risingto 65° before being controlled by cooling. The mixture was thendistilled in a spinning band still. 19.9 g of2-ketopentafluoropropanesulfonic acid was obtained representing a yieldof 27%, bp 47-45 at 0.9 mm pressure.

EXAMPLE 4 Transesterification of Ethyl 2-KetopentafluoropropaneSulfonate to 2-Ketopentafluoropropanesulfonic Acid

25.6 g (0.10) mol of ethyl 2-ketopentafluoropropanesulfonate was stirredat 25° while 17.1 g (0.15 mol) of trifluoroacetic acid was added. Themixture was allowed to stand overnight, then heated on a spinning bandstill to reflux at 60°. Fractional distillation of the reaction mixtureat pot temperatures below 100° and at a pressure of 2.6 mm resulted inthe isolation of 18.4 g of 2-ketopentafluoropropanesulfonic acid,representing a yield of 81%, bp 73°.

EXAMPLE 5 Copolymerization of 2-Ketopentafluoropropane Sulfonic Acidwith Vinylidene Fluoride (VF₂) ##STR8##

A 10-ml stainless steel tube was charged with 3.41 g (0.015 mol) of2-ketopentafluoropropanesulfonic acid, 0.50 ml of 8% perfluoropropionylperoxide in F113, 2 ml of F113, and 3.5 g (0.055 mol) of vinylidenefluoride, then heated at ca. 40° for 8 hr. Evaporation of volatilesunder nitrogen followed by evacuation at 25° (<0.5 mm) overnight left3.5 g of greasy polymer. Evacuation at 25° (<0.5 mm) over the weekendleft 3.1 g of residue, then at 70° (<0.5 mm) for one day left 2.6 g ofresidual viscous copolymer. The polymer was stirred two times with 10 mlof water at 25° to remove the last of unreacted acid then dried at 25°(0.5 mm) to give 2.6 g of very viscous copolymer. Ir: 2.90 and 6.10(HO), 3.29 and 3.34 (satd CH), 7-10μ (CF,C--OC,SO₂) with unknown C═O at5.66μ. Nmr on a solution in DMSO-d₆ showed ¹⁹ F resonances attributableto CF₃ and OCF₂ along with several other kinds of CF₂, while ¹ Hresonances for CF₂ CH₃, OH, and two areas for CH₂ were observed.

    ______________________________________                                         ##STR9##                                                                                 C, 27.26;                                                                              H, 2.56; S, 5.27.                                        Found:      26.99;   H, 2.63; S, 5.23.                                        ______________________________________                                    

EXAMPLE 6 Copolymerization of 2-Ketopentafluoropropanesulfonic Acid withTetrafluoroethylene (TFE) ##STR10##

Copolymerizations of TFE with 2-ketopentafluoropropanesulfonic acid werecarried out at varying pressures as follows:

A. A cold mixture of 20 ml of F113, 5.0 ml of 8% perfluoropropionylperoxide in F113, and 4.6 g (0.02 mol) of2-ketopentafluoropropanesulfonic acid was charged into an 80 mlHastelloy®-lined tube, and 20 g (0.20 mol) of tetrafluoroethylene wasadded at -48°. As the tube warmed slowly, an exothermic polymerizationstarting near 8° carried the pressure to a maximum of 450 psi. Themixture was then heated at 30° for 2 hr. Product polymer was stirredwith 50 ml of F113 and filtered, and the filter cake was thoroughlyrinsed with F113. The polymer was then stirred with 150 ml of water,filtered and dried at 100° under vacuum. There was thus obtained 16.8 gof sulfonic acid. A gram of the solid polymer was stirred with conc. NH₄OH for 3 hr, filtered, and dried under vacuum at 25°. Sulfur analysis ona large sample gave S, 0.07%, corresponding to an equivalent weight of46,000 and a ketosulfonic acid content of 0.5%, n in the general formulabeing 460.

B. A copolymerization similar to the above was carried out with 20 ml ofF113, 2.0 ml of 8% perfluoropropionyl peroxide in F113, 22.8 g (0.10mol) of 2-ketopentafluoropropanesulfonic acid, and 20 g (0.20 mol) oftetrafluoroethylene. The tube was pressured to 500 atm. with argon whilestill cold. As the reaction warmed to 6°, rapid polymerization caused apressure increase and part of the gases was bled off. The productpolymer was extracted with several portions of F113 and dried undervacuum to a colorless solid. A sample treated with conc. NH₄ OH, washed,and dried under vacuum showed on analysis 0.85% S.

C. Reaction of 40 ml of F113, 1.0 ml of 8% perfluoropropionyl peroxidein F113, 22.8 g (0.10 mol) of 2-ketopentafluoropropionyl peroxide, and20 g (0.20 mol) of tetrafluoroethylene was carried out in a 125-ml tubelined with stainless steel under 2500 atm. of nitrogen. The tube waswarmed slowly to 30° and kept at 30° for 4 hr. Work-up of the polymer byextractions with F113 and with water gave 13.9 g (69%) of solidcopolymer. A sample which was stirred with conc. NH₄ OH, washed anddried was analyzed for N and S. For N, 0.12 and 0.15% correspond to anequivalent weight of 10,777 or 2.3% of ketosulfonic acid as the ammoniumsalt. For S, 0.18 and 0.10% correspond to an equivalent weight of 22,900of 1.1% of comonomer, n in the general formula being 105.

D. Samples of copolymer prepared under different pressures as above anda control sample of essentially undyeable polytetrafluoroethyleneprepared in the same system as the copolymers were exposed to the basicdye, Sevron® Red GL. After exhaustive washing, the level of color in thepolymer was taken as a rough measure of comonomer content. The fact thatdyeing occurs is not only a demonstration that the comonomer containingan acid receptor site has been incorporated, since the control is notdyed under the same conditions, but also a useful property.

The general procedure was to stir 1.0 g of polymer with 50 ml of 1:1 H₂O/ethanol containing an excess of Du Pont Sevron® Red GL. After 3 days,the polymer was recoverd, stirred with portions of 1:1 H₂ O/ethanoluntil dye was no longer being extracted (total of 4 washings), and driedunder vacuum.

    ______________________________________                                        Substrate           Result                                                    ______________________________________                                        polytetrafluoroethylene                                                                           essentially colorless                                     copolymer (100-400 psi)                                                                           pale orange-red                                           copolymer (500 atm. and                                                        neutralized with NH.sub.4 OH)                                                                    moderate depth orange-red                                 copolymer (2500 atm)                                                                              strongly orange-red                                       ______________________________________                                    

EXAMPLE 7 Copolymerization of 2-Ketopentafluoropropanesulfonic Acid withVinylidene Fluoride

A. A sample of ester IV was prepared separately from2-ketopentafluoropropanesulfonic acid and vinylidene fluoride. ##STR11##

A metal tube containing 23.8 g (0.10 mol) of sulfonic acid cooled below-40° and 13 g (0.20 mol) of vinylidene fluoride was added. The mixturewas shaken as it warmed to 25° and was kept at 25° for 4 hr.Distillation of the liquid product gave 20.4 g (70%) of ester IV, bp62°-63° (50 mm). Ir (CCl₄): 5.54 (C═O), 6.96 (SO₂ O), and 7.5-94 (CF,SO). Nmr: ¹ H 2.06 ppm (t,J_(HF) 14.3 Hz, CH₃); ¹⁹ F-58.3 (q, J_(HF)14.3 Hz into t, J_(FF) 7.1 Hz, 2F, OCF₂),-75.0 (t,J_(FF) 8.0 Hz, 3F,CF), and -106.1 ppm (q, J_(FF) 8.0 Hz, into overlapping triplets, J_(FF)7.1 Hz, 2F, CF₂ SO₂).

Anal. Calcd for C₅ H₃ F₇ O₄ S: C, 20.56; H, 1.03; F, 45.52. Found: C,20.73; H, 1.03; F, 45.72.

B. Monomer IV from A was copolymerized with vinylidene fluoride asfollows:

A cold mixture of 20 ml of F113, 5 ml of 8% perfluoropropionyl peroxide,and 10.9 g (0.037 mol) of IV was loaded into an 80-ml Hastelloy®-linedtube. After 20 g (0.32 mol) of vinylidene fluoride was added at -40°,the mixture was shaken while it warmed to 25°. After 20 hr at 25°,volatiles were removed under reduced pressure to leave 25.8 g (83% basedon a content of 64% vinylidene fluoride) of white solid copolymer. Asample was stirred with 250 ml of water for 4 hr, filtered and driedunder vacuum. Ir (KBr): similar spectrum to that of poly(vinylidenefluoride), with broadened bands and additional absorptions also present;a 5.6μ band suggests some C═O or C═CF₂ present.

Anal. Calcd. for 8.5 vinylidene fluoride copolymer: C, 31.59; H, 2.41;S, 3.83. Found: C, 31.79; H, 2.60; S. 3.93.

The analysis corresponds to a value of n of 8.5 and 36% by weight ofcomonomer IV. The water-washed polymer was a solid capable of beingshaped or molded at elevated temperatures. In addition, a sample wasdyed with Sevron® Red GL in the same manner as described above. A deepred-orange dyeing was obtained.

UTILITY EXAMPLE A

All the novel acids of this application are very active cationicinitiators, e.g., for tetrahydrofuran (THF) polymerization. A bulkpolymerization was run at ca. 25° on 10 g of purified THF with 0.31 g of2-ketopentafluoropropanesulfonic acid as initiator. Viscosity increasedmarkedly in 30 min, but the polymerization was allowed to proceed forone day. Work-up was by quenching with 50 ml of concentrated ammoniumhydroxide in 50 ml of distilled water followed by drying at 50° underfull pump vacuum. A yield of 7.54 g of colorless, solidpolytetrahydrofuran was obtained: η_(inh) (0.1% in (CF₃)₂ CHOH at25°)=0.80.

Polytetrahydrofuran is a hydrolytically stable soft segment with goodlow temperature properties for incorporation into polyurethanes usefulas elastomers and as spandex fibers. For example, F. Rodriquez,"Principles of Polymer Systems", McGraw-Hill, New York, N.Y., 1970, p.424 cites homopolymers of tetrahydrofuran in the mol. wt. range1000-3000 as useful components with diisocyanates.

I claim:
 1. A solid, moldable, dyeable copolymer of the formula ##STR12## wherein the comonomer is ethylene, vinyl fluoride, vinylidene fluoride, tetrafluoroethylene or trifluoroethylene, R is H or CF₂ CH₃ and n is 2-500.
 2. The copolymer of claim 1 in which the comonomer is vinylidene fluoride, tetrafluoroethylene or trifluoroethylene.
 3. A solid, moldable, dyeable copolymer of vinylidene fluoride and 2-ketopentafluoropropanesulfonic acid.
 4. A solid, moldable, dyeable copolymer of tetrafluoroethylene and 2-ketopentafluoropropanesulfonic acid. 